Devices and techniques for detecting faults in photovoltaic systems

Abstract

Devices and techniques for detecting faults (e.g., ground faults) in photovoltaic (PV) systems are provided. A fault-detection impedance component may be included in a PV system on the path to equipment ground. The PV system may determine whether a ground fault exists based, at least in part, on a measured impedance between a conductor of the PV system and a ground node of the PV system, and on a reference impedance. When it is determined that a ground fault exists in the PV system, action may be taken to mitigate the ground fault.

What is claimed is: 
     
         1 . A method of determining whether a fault exists in a photovoltaic system, the method comprising:
 determining whether a ground fault exists based, at least in part, on a measured impedance between a conductor of the photovoltaic system and a ground node of the photovoltaic system, and on a reference impedance; and   when it is determined that a ground fault exists in the photovoltaic system, mitigating the ground fault.   
     
     
         2 . The method of  claim 1 , wherein determining whether the ground fault exists comprises comparing the measured impedance to the reference impedance. 
     
     
         3 . The method of  claim 1 , wherein determining whether the ground fault exists comprises determining whether the measured impedance is less than the reference impedance or less than a specified percentage of the reference impedance. 
     
     
         4 . The method of  claim 1 , wherein the reference impedance depends on an impedance along a path between the conductor and the ground node, and wherein the path includes a ground fuse. 
     
     
         5 . The method of  claim 4 , wherein the path further includes a fault-detection impedance component. 
     
     
         6 . The method of  claim 5 , wherein the fault-detection impedance component comprises a reactive impedance portion. 
     
     
         7 . The method of  claim 5 , wherein the fault-detection impedance component includes an inductor, and wherein a core of the inductor comprises a ferrite core, a ferromagnetic core, and/or an air core. 
     
     
         8 . The method of  claim 4 , wherein the reference impedance is between 5% and 90% of the impedance along the path, between 5%, and 80% of the impedance along the path, between 5% and 70% of the impedance along the path, between 5% and 60% of the impedance along the path, between 5% and 50% of the impedance along the path, between 5% and 40% of the impedance along the path, between 5% and 30% of the impedance along the path, between 5% and 20% of the impedance along the path, between 5% and 10% of the impedance along the path, less than or equal to 10% of the impedance along the path, less than or equal to 5% of the impedance along the path, or less than or equal to 1% of the impedance along the path. 
     
     
         9 . The method of  claim 1 , further comprising determining the measured impedance between the conductor and the ground node. 
     
     
         10 . The method of  claim 9 , wherein determining the measured impedance between the conductor and the ground node comprises determining an impedance between two nodes along an electrical path between the conductor and the ground node. 
     
     
         11 . The method  claim 1 , wherein mitigating the ground fault comprises presenting a message relating to the fault. 
     
     
         12 . The method of  claim 1 , wherein mitigating the ground fault comprises signaling an inverter of the photovoltaic system to cease commutation and/or to open protection disconnects. 
     
     
         13 . The method of  claim 1 , wherein mitigating the ground fault comprises deactivating one or more photovoltaic cells. 
     
     
         14 . A device configured to couple one or more photovoltaic cells to an inverter, the device comprising:
 a terminal configured to couple one or more photovoltaic cells to an inverter via a conductor, the conductor being coupled to a ground node by a fuse circuit; and   a fault-detection impedance component coupled to the conductor in series with the fuse circuit.   
     
     
         15 . The device of  claim 14 , wherein the fault-detection impedance component is coupled between the fuse circuit and the terminal, or between the fuse circuit and the ground node. 
     
     
         16 . The device of  claim 14 , wherein the fault-detection impedance component comprises an inductor. 
     
     
         17 . The device of  claim 16 , wherein the inductor comprises a ferrite core, a ferromagnetic core, and/or an air core. 
     
     
         18 . The device of  claim 14 , further comprising one or more components configured to measure an impedance between the conductor and the ground node. 
     
     
         19 . A photovoltaic system comprising:
 an inverter;   one or more photovoltaic cells coupled to the inverter via a conductor, the conductor being coupled to a ground node of the photovoltaic system by a fuse circuit; and   a fault-detection impedance component coupled to the conductor and in series with the fuse circuit.   
     
     
         20 . The photovoltaic system of  claim 19 , wherein the fault-detection impedance component comprises an inductor.